The portable machine tools of the present day endowed with such an electric motor for their operation are to be used by an operator driving the primary motion of the tool through the electric motor in a suitable way, as a function of the situation in which the tool itself turns out to find itself time by time.
The driving of the machine tool is therefore carried out by the operator, based upon how he "feels" the situation of the tool time by time.
For instance, the electric motors of drills are endowed with a control circuit scheme including triacs, diacs, passive components and so on, with a variable resistive component which is inserted through a button to be pressed to modulate the speed of revolution of the tip of the drill.
The portable machine tools of the present day are thus endowed with simple means for intervening on the primary motion of the machine tool, but the drive remains deputed to the sensitivity, the processing and the intervention of the operator.
However, the proceeding on the feeling of the operator in the drive of the primary motion of the tool of the machine renders the machining exacting and the results of the same potentially not much precise.